Inkjet (IJ) recording technologies have met with developments of general technologies, including various peripheral technologies; such as hardware such as inkjet heads, and printer systems; supplies such as ink media; and controlling methods for controlling image treatment, and other systems, and thereby achieve high quality images which may be superior to those of a silver halide photograph at present, and are established as IJ printing technologies. The IJ printing technologies using aqueous inks and porous media are widely used among general consumers because of their handiness, as disclosed particularly in Patent Literatures (PTLs) 1 and 2,and are in the recent years used such that the silver halide photographic method may be replaced by the IJ printing technologies. Accordingly, these IJ technologies are increasingly used in the field of printing industries. There are generally two applications of the IJ technologies in the printing industries at present.
One of the applications is in so-called “horizontally developed” technologies which are widely used among general consumers. This is an application where a small amount of high quality images is printed on IJ media, regular paper, and the like, and the application is represented by use of a proof machine using a wide format printer and use for forming signs. The IJ printing technologies have met with a great success with respect to this application and a very large market for this application has been already established.
The other of the application, which especially attracts attention recently, is an application in so-called variable printing which is capable of printing at very high speed, though which does not require a press plate. So far, the application of the IJ printing technologies in such variable printing has been studied and put into practical use since a long time ago as disclosed in, for example, PTLs 3 and 4,and is so far mostly applications in the field in which relatively high image quality is not required, such as in the field in which mainly letters and rules are printed, such as for fee specifications, issued invoices, and address printing.
That is, for example, PTL 3 discloses an inkjet recording sheet having an offset printing layer on one side of base paper, and an inkjet recording coat layer on the other side, wherein the base paper is subjected to surface coating and size press treatment with a size press liquid containing, for main components, 0.5 g/m2 to 3.0 g/m2 of an aqueous polymer resin (a cation resin described below or a normal starch-based size agent capable of preventing elution of an aqueous polyvalent metal salt), 0.1 g/m2 to 2.0 g/m2 of a cation resin (for improving water resistance of a dye ink and print density of a pigment ink), and 0.1 g/m2 to 2.0 g/m2 of an aqueous polyvalent metal salt chelating agent (for improving ink absorption and preventing neighboring ink spots having different colors from bleeding and overlapping); and thereby improving ink absorption and at the same time keeping a sizing degree of the base paper low in inkjet recording on one side; and thereby preventing degradation of print resistance with an excessive absorption of dampening water at the time of offset printing on the reverse side, at the same time preventing exuding of inks at the time of writing on the reverse side with a fountain pen or an aqueous ink pen, and preventing degradation of offset printing or print resistance in printing on the reverse side of the base paper which degradation is due to elution of a cationic material used for improving water resistance of a dye ink or improving print density of a pigment ink in offset printing. However, this base paper does not have an ink absorption layer produced by a cast coating method, thus, cannot achieve a glossy inkjet record. In addition, this invention has two types of printing surface, that is, an offset printing surface and an inkjet recording surface each on one side of the paper, and this invention does not described an application in electrophotography.
PTL 4 discloses printing coated paper having on a surface of base paper a first coat composed of 1.0 g/m2 to 2.0 g/m2 of a cationic material (an alkylamine/ammonia/epichlorohydrine polycondensate which has a molecular weight of 20,000 or less and is capable of reacting with an anionic site of inks of an inkjet aqueous ink which contain a direct dye or an acid dye), and a second coat produced on the first coat with a coating liquid containing a SBR latex binder, which does not contain an aqueous resin but contains 20% by mass or more of an acrylonitrile component portion, and 30% by mass or more of light calcium carbonate as a pigment, wherein the coated layers are super-calendered such that an on-demand inkjet print part can be formed on blank space of an offset print part as required. However, also this coated paper does not contain an ink absorbing layer produced by a cast coating method, thus, cannot achieve a glossy inkjet record. In addition, an application in electrophotography is not mentioned in this patent application.
PTL 5 discloses an inkjet recording medium having a normal undercoat layer which is on a substrate, and an ink absorbing layer produced by a cast coating method (a glazed finish of the coat surface produced with a heated mirror drum) on the under coat layer, wherein the ink absorbing layer is formed with a coating liquid, and the coating liquid contains a precipitated silica, which has a relatively low BET specific surface area(81 m2/g to 200 m2/g), a relatively low oil absorption amount (144 ml/100 g to 200 ml/100 g), and a particle diameter not excessively small (particle diameter: 1.3 μm to 2.3 μm), and which is selected from silica pigments that have hiding power stronger than those of other body pigments, have a transparent appearance, a high BET specific area, and a large oil absorption amount, thus, have excellent ink absorption and color developing ability, with the precipitated silica being added into the coating liquid in an amount of 60% by mass to 80% by mass of the under coat layer, and contains a binding agent which is incorporated in the coating liquid in a semi moist state immediately after production in an amount of 3% by mass to 50% by mass per 100 parts by mass of the total pigment, thereby the binding agent preventing secondary aggregation caused by its high activity in the coating liquid and avoiding excessively high viscosity of the coating liquid, and wherein the ink absorbing layer is made uniform thereby.
However, this inkjet recording medium has an undercoat layer and indirectly achieves high ink absorption using the silica body pigment, making it difficult to produce color images having deeply toned colors that can be produced by an adequate penetration of the ink in the depth direction into the ink coated layer.
These originate from weak points intrinsic to the IJ technologies.
In addition to the above Patent Literatures, PTL 6 discloses offset paper having a coated layer casted according to a casting method using an aqueous coating liquid containing, at the time of preparing the coating liquid, 3% by mass to 30% by mass of a body pigment that does not have a high oil absorption amount measured according to JISK-5101 (oil absorption amount thereof: 70 ml/100 g to 280 ml/100 g) as a pigment excellent in dispersibility (such as white carbon, diatomaceous earth, calcined diatomaceous earth, calcined clay, flux calcined diatomaceous earth, fine particulate anhydrous aluminum hydroxide, fine particulate titanium oxide, fine particulate anhydrous silica, magnesium carbonate), and 3% by mass to 30% by mass of a styrene-butadiene-methyl methacrylate terpolymer latex which is produced by copolymerizing a methyl methacrylate component in a mass ratio of the methyl methacrylate component to a styrene-butadiene copolymer portion of 10% by mass to 40% by mass in the styrene-butadiene copolymer which is characterized in its excellent adhesion strength and hardness of a film thereof. According to this Patent Literature, this technology can prevent ink piling at the time of offset rotary printing using a polychromatic printing system (a phenomenon in which ink deposited on a paper surface with the first trunk of a blanket is reverse transferred onto the second or later trunk of the blanket, thereby reducing image density of the printed matter in a corresponding manner, or in the severe case, making the ink piled up and making the reverse transferred ink retransferred onto printed matter to produce contamination) because of the existence of a methyl methacrylate component in the ink absorbing layer. Use of the inkjet printing method is not considered in this technology, and no electrophotograqphical application of the invention of this patent application is described in this patent application.
Most of the present IJ technologies are those in which drops of a low-solid-content ink are ejected from a head, attached in a liquid state on a medium, and then dried and solidified according to some method. IJ technologies for general consumers or wide format IJ technologies depend on ink absorption of a medium for most part of the ink drying. It is very difficult to realize both of the ink drying and high speed printing in a balanced manner, without using IJ media or regular paper.
Especially in the field of variable printing among the fields of these industries, expensive IJ paper which is preferable for general consumer's use or for use in some proof machines has not been used very much because of very hard limitations on the use of this product set by factors of productivity and printing cost. Therefore, as a result of making ink drying ability and costs first priority, only regular paper has been available in the field of variable printing so far. Especially for printing in which high quality glossy images are desired, such as for printing high-grade catalogs, fancy boxes, magazine covers, or direct mails, only realistic measures for using high-speed inkjet printing have been using very expensive media. On the other hand, when cheap regular paper is used, it is difficult to produce high quality images because that ink dots spread on the paper and that the ink penetrates the paper so severely that high density images are not reproducible. When so-called “IJ printers for general consumers” are used and images are printed at high speed, it is impossible to reproduce, at a low cost, high quality printed matter such as those printed on IJ glossy paper.
While the IJ method and IJ glossy paper begin to be partly used in minilab for industrial purpose, from the view point of difficulty in use the practical use of the above medium is for use in DPE where consumers may purchase the printed matter printed on the above medium in spite of a relatively high unit cost of printing, at present, because of a still high price of the above medium. Therefore, at present, in order to practically use these IJ photoprinting methods in industrial fields, it is necessary to reduce the cost of the above medium in some way.
IJ media mainly for expected photographical use such as those mentioned above are, at present, mainly classified into RC glossy paper produced by laminating absorbing layers on resin coat (RC) paper as base paper, and IJ cast coated paper which uses, as base paper, high quality paper or coat paper surface layer of which is mirrored according to a cast coating method. The IJ cast coated paper, which uses cheaper base paper and achieves higher production efficiency than the RC glossy paper than the RC glossy paper, can be produced to some extent at a lower cost than the RC glossy paper, however, needs to be equipped with an ink absorbing layer using raw materials for IJ cast coated paper so as to achieve both excellent ink absorption and high glossiness, and thus is inadequate for use in usual commercial printing because of a still-high cost thereof.
In addition, it is known that when offset printing or electrophotographic printing is performed with respect to these IJ media, various problems are known to occur. In the case of offset printing, an acid component contained in the IJ media is well known to disadvantageously cause contamination of blocks and poor ink fixation. In the case of electrophotographic printing, the media is well known to fuse in the heater configured to fix toner and, thereby, cause machine failure.
Also conventional IJ media themselves may cause, because of the limitations on materials which can be used in the ink absorbing layer, powder down at the time of media cut and cracking of a coat film at the time of paper folding in bookbinding, and thus they can be said to have been media difficult to use in the industrial fields.
Accordingly, IJ glossy paper is rarely used in large amounts for industrial purposes at present.
On the other hand, the above-mentioned cast coating paper is representative glazed paper that is used in large amounts in printing industries and is used in general offset printing, and the like. However, the above-mentioned cast coating paper for offset printing is not equipped with an absorbing layer for absorbing an ink, which is different from the cast coating paper for IJ printing, and could not be used for IJ printing application. When images are inkjet printed on normal commercial printing coat paper, the ink absorption and wettability of the resulting printed matter are degraded, and the images spread and the printed matter becomes difficult to dry, making the use of the normal commercial printing coat paper for inkjet printing impractical.
A printing medium which can be used in every printing method is desired in the variable printing. When the variable printing is used, it becomes possible to offset print a basic area in the pages, which is not required to be offset printed, in large number at a low cost, and to print other area in the pages according to at least one of an electrophotographic method or an inkjet method. Also from the viewpoint of reduction of productive/economical risk of insufficient selection of the similar types of goods which are produced by a media maker for different printing method the goods use, a mighty medium which can be used in various printing methods is desired.
However, there have been no medium that can be used in all of electrophotography, offset printing, and inkjet printing, except regular paper.
Particularly, it has been considered technically very difficult to produce, at a low cost, a medium that can be used in all the printing methods and can produce glazed surfaces. Because the realization of such media will dramatically widen the range of applications of the variable printing, such media has been strongly desired.
The present inventors tested an inkjet recording method that can reproduce, at a low cost, texture of the recorded matter similar to those of silver halide photographs, so as to use the inkjet recording method using an aqueous pigment in commercial printing, particularly, in photographic image quality printing in which high quality images are desired.
The present invention discloses an example in which a pigment ink having high penetration ability, such as those described in PTL 7,is used in combination with a medium having a low ink absorption, which is in contrast to the conventional media, to realize an image forming method that can be used at a low cost on commercial printing paper, and the like. It becomes possible, by this method, to inkjet print even on such low-ink-absorption paper as commercial printing paper or publication printing paper which has been considered inappropriate for inkjet printing.
However, it has been difficult to print a quality photograph having a glazed surface at a practical speed in variable printing even when this method is used. The cast coating paper has excessively poor ink absorption among many types of commercial printing paper, exuding images when images are printed at a high speed, producing image degradation that can not be neglected when high quality photographic images are reproduced, making the use of the cast coating paper impractical.
Furthermore, regarding coated layers on the base paper, the present inventors have, so far, proposed an inkjet recording method (PTL 8) including at least printing on a recording medium with an aqueous ink, wherein the recording medium is composed of a support containing cellulose pulp as a main component, and one or more of coated layer is deposited on at least one side of the support, the coated layer contains a pigment and an adhesive, the amount of cationic additives in the total amount of materials forming the coated layer is 0.1% by mass or less, the 60° glossiness of the most outer layer of the recording medium as defined in JIS-ZS-8741 is 13 or less and the cut off value of the most outer layer of the recording medium is 0.8 μm, and wherein the aqueous ink contains at least particulate color material, resin emulsion, water, and a moistening agent, and the solid content of the aqueous ink is 3% by mass or more. However, it is necessary to investigate compatibility of the coated layer with the base paper supporting the coated layer in addition to the coated layer.